Effect of annealing on the interface microstructure and mechanical properties of a STS-Al-Mg 3-ply clad sheet

In this study we investigated the influence of post-rolling heat treatment upon the microstructure evolution at interface and subsequent uniaxial tensile properties of roll-bonded ferritic stainless steel (STS430)-aluminum (Al3004)-magnesium (AZ31) 3-ply clad metal. By utilizing optical, scanning electron and transmission electron microscopes, the generation and growth of interlayer consists of γ (Mg17Al12) and β (Mg2Al3) phases was verified between the constituent layers in the Mg/Al with total thicknesses of 4.56 and 11.21 μm during annealing at 300 °C for 1 and 3 h, respectively. Although as-rolled clad metal was somewhat joined by mechanical locking at the interface, annealing-induced generation of thin diffusion layer between AZ31 and Al3004 by annealing at 300 °C for 1 h resulted in the enhancement of uniaxial tensile properties in terms of elongation. However, further annealing for 3 h lead to weakening the interface bonding properties due to the significant generation of brittle intermetallic phases. The mechanism for retarding interface delamination along the direction of tensile axis was confirmed by the observation from the side surfaces of ex-situ stepped tensile-test specimens.